The present invention relates to a two-cycle engine oil composition, and more particularly to a two-cycle engine oil composition having excellent high-temperature detergency and anti-seizure property which can contribute to an improvement in the output of an engine. 2. Prior Art
In recent years, racing has been extensively conducted under the stimulus of popularity of sports motorbikes. A racing engine is required to have a compact size, light weight and high output as compared with usual engines. Heightening of output has been achieved through improvements in suction and exhaust systems and the shape of the combustion chamber as well as the enhancement of engine speed for maximum output. It would be significant if a lubricating oil to be used in the racing engines could also contribute to an improvement in the output.
At the present time, for a two-cycle engine for racing, a special oil comprising a base oil composed of a synthetic ester oil having excellent thermal stability is used for the purpose of retaining an oil film at a high temperature. The present inventors have found that such an oil brings about a lowering in the output during the operation of the engine. It has been confirmed that like such a two-cycle engine oil comprising a synthetic ester oil as the base oil, two-cycle engine oils comprising a mineral oil and a polybutene as the base oils also bring about the above described phenomenon of the lowering in the output. Therefore, the lubricating oil has been regarded as impossible to contribute to an increase in the output of the two-cycle engine.
Under these circumstances, the present inventors had examined various synthetic oils and have made extensive and intensive studies with a view to developing a lubricating oil suitable for a two-cycle engine and, as a result, have found that an oil incorporating a particular base oil and additive can remarkably improve the output over two-cycle engine oils which have hitherto been put on the market and yet brings about no lowering in the output.